[LARTC] Changing default route for an entire subnet/NIC

[LARTC] Changing default route for an entire subnet/NIC

[brian]

Greetings,

If you look at Section 4.1 of the howto, they give  asimple example of changing the default
route for a single IP address by doing the following

# echo 200 John >> /etc/iproute2/rt_tables
# ip rule add from 10.0.0.10 table John
# ip route add default via 195.96.98.253 dev ppp2 table John
# ip route flush cache

I'm trying to do something very similar, except that I want to route an entire class C subnet
out a different NIC card in my firewall..

I did the exact same thing as above except used the line

ip rule add from 192.168.0.1/24 table John
ip route add default via 192.168.1.1 dev eth4 table John

This doesn't work, what happens is that the entire subnet loses conect with the firewall, so DNS
lookups fail and I basically can't go anywhere. Using just one IP like the example above seems
to work fine..

Any ideas?

_______________________________________________
LARTC mailing list / LARTC@mailman.ds9a.nl
http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/

Re: [LARTC] Changing default route for an entire subnet/NIC

[Brian Weaver]

Oops, made a mistake in my example,
I actually enter
ip rule add from 192.168.0.0/24 table John

As soon as I do this, that subnet loses all contact with my firewall, so it can't DHCP an address,
do DNS servers, ping, anything.. 

Any clues?


brian@fcu.com <brian@fcu.com> [2003-12-17 22:34:14 -0700]:
> Greetings,
> 
> If you look at Section 4.1 of the howto, they give  asimple example of changing the default
> route for a single IP address by doing the following
> 
> # echo 200 John >> /etc/iproute2/rt_tables
> # ip rule add from 10.0.0.10 table John
> # ip route add default via 195.96.98.253 dev ppp2 table John
> # ip route flush cache
> 
> I'm trying to do something very similar, except that I want to route an entire class C subnet
> out a different NIC card in my firewall..
> 
> I did the exact same thing as above except used the line
> 
> ip rule add from 192.168.0.1/24 table John
> ip route add default via 192.168.1.1 dev eth4 table John
> 
> This doesn't work, what happens is that the entire subnet loses conect with the firewall, so DNS
> lookups fail and I basically can't go anywhere. Using just one IP like the example above seems
> to work fine..
> 
> Any ideas?
> 
> _______________________________________________
> LARTC mailing list / LARTC@mailman.ds9a.nl
> http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/
_______________________________________________
LARTC mailing list / LARTC@mailman.ds9a.nl
http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/

Re: [LARTC] Changing default route for an entire subnet/NIC

[Martin A. Brown]

Brian,

 : Oops, made a mistake in my example,
 : I actually enter
 : ip rule add from 192.168.0.0/24 table John
 :
 : As soon as I do this, that subnet loses all contact with my firewall,
 : so it can't DHCP an address, do DNS servers, ping, anything..

Perhaps what you wish to do is copy the entire main routing table to the
table "John" [0] and then change the default route in that table.

Try:

   # copy_routing_table John
   # ip route change table John default via $OTHER_GATEWAY

This is a simple application of policy routing.  Another possibility is to
exclude 192.168.0.0/24 from the rule itself:

   # ip rule add from 192.168.0.0/24 table John
   # ip rule add from 192.168.0.0/24 to 192.168.0.0/24 table main

You may wish to consider adding the prio keyword explicitly.  See also
some documents I have written in which I attempt to explain the policy
routing system in plain terms [1].

Good luck,

-Martin

  [0] http://linux-ip.net/html/scripts/copy-routing-table.sh
  [1] http://linux-ip.net/html/ch-routing.html

-- 
Martin A. Brown --- SecurePipe, Inc. --- mabrown@securepipe.com

_______________________________________________
LARTC mailing list / LARTC@mailman.ds9a.nl
http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/